Wireless power or energy transfer is directed to the transmission of electrical energy from a power source to an electrical load without the use of conductors. Wireless power transfer can be achieved using a various power transmission technologies using time-varying electric, magnetic, or electromagnetic fields. Wireless power transfer can be particularly useful in situations where the use of conductors is inconvenient or dangerous, for example, to transfer power.
For near-field (i.e., non-radiative) wireless power transfer, inductive coupling is widely used and its applications include providing power to charge electric toothbrushes, radio-frequency identification (RFID) tags, smartcards, and implantable medical devices. Recently, more emphasis has been placed on the development of wireless power transfer systems for charging mobile and handheld computing devices.